\begin{figure}[tpb]
\begin{center}
%\subfigure[HBase architecture]{
%  \includegraphics[width=3in]{figures/hbase-arch}
%		\label{fig:hbase-arch}
%}
%\subfigure[\sys architecture]{
  \includegraphics[width=1\textwidth]{figures/exalt-arch}		
%}
\end{center}
\caption{The architecture of \sys. \sys differs from HBase
  in three key ways. First, \sys' block driver performs end-to-end
  checks to validate each \get reply. Second, \sys performs pipelined
  commit across different key regions to ensure ordered commit. Third, \sys replicates region servers via active
  storage to eliminate spurious state updates. For efficiency,
  Salus tries to co-locate the replicated \rs{s} with the replicated \Dn{s}
  (\DN{s}). }
\label{fig:exalt-arch}
\end{figure}


